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An impressive 120 watt amplifier circuit can be built by cascading a couple of TDA 2030 IC in a bridged tied load (BTL) configuration and through a few current boosting transistors.

Advantage of a BTL Amplifier Topology

The main objective of a BTL configuration is to enable a two way operation of the load which in turn helps to increase a two fold increase in the efficiency level of the system. It's equivalent to a full bridge network which we normally find in inverters.

The complete circuit diagram for the proposed BTL 120 watt amplifier circuit using two TDA 2030 ICs can be seen in the above diagram.

Circuit Description

IC1 and IC2 are the two TDA2030 ICs rigged in a bridged tied load configuration which means the these two IC s now conduct in tandem in response to the high and low amplitudes of the input frequency and drive the loudspeaker in a powerful push pull mode.

For example when IC1 output may be delivering a high output to the speakers, IC2 simultaneously would be delivering a low output and vice versa enabling the required push pull action on the loudspeaker. This means the loudspeaker would be alternately operated with maximum positive and negative supply levels, causing the loudspeaker to work with double efficiency level compared to the normal amplifiers which are not BTL based.

The BJTs T1---T4 are included to boost the current level of the amplifier upto the specified 120 watt RMS, since the IC1, IC2 alone wouldn't be able to do this.

The NPN/PNP output BJTs also complement the BTL topology and help the ICs to achieve the specified amount of power on the loudspeakers.

The various resistors and capacitors around the speaker are introduced to suppress and filter the final outcome on the speaker, and to produce a clean and distortion free audio on the speaker.

Dual Power Supply for the Amplifier

The power supply for this 120 watt BTL amplifier using TDA2030 ICs is derived from a 12-0-12V / 7 amp transformer. whose output is rectified using a bridge rectifier and filtered using the indicated capacitor C8---C11.

The power supply produces a dual +/- 20V / 7 amp output which is mandatorily required for most BTL based amplifier circuits.

In this post we learn how to make a simple 150 watt power amplifier circuit using a typical OCL design which ensures cheap layout and use of minimum components, with high reliability.

Introduction

Referring to the figure a perfectly symmetrical OCL based amplifier can be seen , using discrete components suitable for all electronic enthusiasts and hobbyists for going through an in-depth practical study with its topology.

This OCL amplifier circuit is a mid-range power amplifier capable of delivering a good 150 watts of power due to its symmetrical structure, wide frequency response, simple layout and so on. The sound quality will be quite satisfactory, and comparable to other equivalent high-fidelity amplifiers normally preferred by the users for home use.

How the amplifier circuit works

The first stage of the circuit can be seen built with a complementary symmetrical differential configuration, each of the BJT channels using 2SC1815, 2SA1015 consume about 1mA, while in the quiescent state

The next stage is designed for handling the voltage amplification and this also makes use of a complementary push-pull design, through a set of high power complementary pair of BJTs namely A180, C180, which runs using a current of about 5mA.

The two 1N4148 ensure a drop of 1.6V required for biasing the relevant bases of the complementary BJTs.

The next two complementary power BJTs involving TIP41C, TIP42C create the driver stage or the intermediate buffer stage fo the last power transistors.

The inclusion of this high efficiency buffer/driver stage becomes one of the main features of the modern OCL amplifier design, which helps to offer a high load impedance, and thereby ensures a very stable Higher gain amplifier output stage.

Additionally this type of capacitor less topology also ensures a lower output resistance across the output power transistor stage, which in turn helps the output junction capacitance Cbe charging rate to become faster, thus improving the overall transient characteristics and frequency stability of the circuit.

However the operating current of this stage can be slightly higher, at around (10-20) mA, for each of the channels which may sometimes go as high as 100mA under higher full volume, this happens because the specified quiescent current may be capable of saturating the output stage to the most optimal levels.

As can be witnessed in the given 150 watt amplifier circuit diagram, the emitter resistances of the driver stage employs a floating termination, and these are not connected with the earth line, and this causes the amplifier to operate typically in the Class A range, and ensure a maximum bias voltage for the output stage.

The power output stage is wired using the traditional complementary capacitor less design and features an FT (frequency transition) level of as high as 60 Mhz, across the BJTs C2922, A1216, through a quiescent current consumption of around 100mA.

The amplifier also employs a negative feedback loop across the output stage and input inverting stage, which sets the amplifier to a gain level of approximately 31.

In the field of audio amplifiers OCL stands for Output Capacitor-Less Amplifier design.

How it Works

In this OCL type of amplifier topology or configuration, the power output stage is directly coupled to its preceding driver stage without coupling capacitors.

The following figure shows a typical OCL amplifier output stage, as can be seen, the VT9/VT10 power BJTs bases are directly linked with the VT7, VT8 BJT stage, and the same can be seen with the earlier stage, wherein no capacitors are involved for the indicated couplings.

Circuit Example

Although there could be many versions of OCL amplifiers, mostly the push-pull type output configurations is popularly employed in OCL designs. as shown above.

Advantages

The OCL configuration could become popular due to some distinct advantages it possesses, compared to the other forms of amplifier topologies. The main features can be learned from the following points:

Elimination of capacitor coupling enables the unit to become very sleek and compact, and also helps to make the design very cost effective.

The OCL design ensures enhanced immunity to the so called "motorboat oscillations" in amplifiers.

The design also allows the unit to deliver high power outputs even at lower input audio frequencies or DC supplies.

Disadvantages

Although OCL amplifiers come with a few great advantages, it may exhibit a couple of marked disadvantages, as given below:

The power devices show a tendency of dissipating significant amounts of power.

In amplifiers where the bias points are poorly controlled, an OCL amplifier could pass the DC content into the loudspeakers, causing heating of the loudspeaker.

In this post we learn about a simple Hi-Fi balanced microphone preamplifier circuit and also evaluate the calculations, specifications of the design through formulas.

What is a Balanced Preamplifier

A "balanced" amplifier or differential amplifier possesses not one but two distinct inputs and only the difference amongst these inputs is actually ampliﬁed.

To elucidate just how this performs please see the diagram that indicates a basic version of a balanced microphone preamplifier circuit. To help make the calculation less difficult we are going to cut down the gain to 9 simply by doing Rl = R4 = and R5 = Rl l = 9.

Circuit Schematic

Typically the units aren't critical. just the proportions are. We are going to commence the justification by exploring the situation wherein input with R1 is at 0V and input with R4 is at + l00mV.

How the Circuits Works

An perfect amplifier will do a couple of stuffs - it will not take virtually any current into the input pins and it keep the output unaffected regardless of any voltage variations at the input pins.

We therefore will need to have 100mV through R4 and therefore a voltage of 900mV around R11 (it possesses 9 times the resistance and the exact same current like R4). This offers us a gain of nine. The output is for that reason -900mV. In the circumstance any time point A reaches 0V and point B is in +100mV. point D is going to be at

VB x R5/(R1 + R9) = 90mV

As a result point C will in addition be at +90mV. The voltage around R4 will probably be 90mV and voltage around Rl is going to be 810mV (9 x 90mV).

This implies the output voltage ought to be +900mV. Also this is with gain of nine. Observe even so that the polarity (or phase) is not equal. At this point imagine both inputs are at say + 1V, point D will probably be at +900mV and thus will point C.

The voltage through R4 is l00mV and R11 900mV This provides an output voltage of (1V The common signal is just not amplified by any means In case however, one input (B) reaches IV and the other (A) was at l.0lV the difference is amplified and the output will probably be -lV.

Returning to the specific circuit, we have employed an LM301A with a pair of low-noise transistors in the front stage.

These transistors come with a constant current through Q3 and Q4. A constant current is necessary because enables the inputs to increase and down without transforming the voltage around R6 or R7

The resistor R2 and R3 relate the inputs to UV are usually high enough never to impact the functioning in the slightest

Circuit Schematics

From the figure we can see that the input signal is connected to the resistor R2, which sets the input impedance of the amplifier at 33K along with the coupling capacitor C2.

The input stage comprises of an ultrasonic filter circuit stage made up C3, R3 and R1 which suppresses any entry of noise through a low RF attenuation.

After this the signal is allowed to pass to pin#7 of the IC enabling a 25 times gain for the signal. This gain is sustained by feeding it back to the input pinout via R5 and R6 and is calculated by the formula (1 + R5/R6)

A frequency cut of -3dB below 10Hz is achieved via C5 which may be seen attached with R5.

The amplified music input is delivered from pin#3 which is ultimately fed to the loudspeaker for the amplified sound generation, however before this can happen, the signal has to pass through a network of R4 and C4 which prevents the amplifier from getting unstable during full loads and thus ensures a continuous stable output under full volume.

Power Supply

The power supply employs a 24-0-24V 5 Amp transformer which is rectified by the indicated bridge rectifier module, and is filtered using C13 and C14.

A simple 50 watt amplifier circuit is explained below, let's learn how to build it at home using this versatile single amplifier chip LM3876T

By: Dhrubajyoti Biswas

Analyzing the Circuit

A good power amplifier is a necessity, especially when it comes to listening music. An amplifier added to a sound system will definitely enrich the quality of music. This project therefore will attempt to give you a detailed insight of making a simple 50 watt power amplifier.

The system that we are going to deal with is primarily based upon the technical specification laid out by National Semiconductors, and following this the result came out well. Easy to build and good output in terms of distortion and noise, the following section will detail the way it is built.

Before we kick-start this development, we have tested the PCB and result came out positive. We have received very good sound quality provided the protection circuitry is not in operational mode.

The last stable version of the board ESP P19 (Rev-B) has few alterations, such as, the connection to the sound impairment monitor [SIM] has been taken out.

The following Figure is a layout of the original board:

Board Layout

Circuit Description

As per the diagram, there is an addition of polyester bypass capacitors and the mute circuit is left disabled, since it is mainly useful when developing a preamp. However, we made some adjustment into the board to provide space for power and input connectors.

As per the above figure, the voltage gain is set to 27dB, and it can be changed by adding resistors of different value for the path of the feedback.

The inductor has 10 turns of enameled copper wire of 0.4mm and is wounded around the body of the 10ohm resistor. The soldered wire lies at the end of the resistor and the insulation should be brushed off on each end.

Our recommendation would be to use 1watt type 10ohm and 2.7ohm resistors. The rest should metal film of 1%. It is also ideal to keep the electrolytic capacitors @ 50V.

For supply, 100nF (0.1uF) should be placed near to the IC in order to avoid oscillation. The voltage supplies to maintain at full load should be around +/- 35 volts, which would produce 56 watts (Max.).

Also to achieve lowest case to the heatsink thermal resistance it is vital to engage max power. This can be done by mounting mica washer with no insulation. However, do keep in mind the heatsink need insulation from the chassis since the heatsink maintain supply voltage of –ve.

The following schematic in Figure shows the changes we made on the original board:

Referring to Figure above, the revised board is very much similar to that of the original one, except some changes by removing some components along with the SIM.

The present on-board decoupling gives great performance. It uses electrolytic of 100nF Polyester and 220uF electrolytic.

Alternatively, you can also use monolithic ceramic capacitor on every rail. While C1 and C2 is referred as polarized electrolytic types, you may use non-polarized electros.

Another option would be to apply on C1 a 1uF polyester cap. If C1 is intended to be used as tweeters you can use small values of 100nF which is good to go ahead.

If you are building the proposed simple 50 watt power amplifier circuit to use it for biamped/triamped system tweeter or midrange, the C1 valued need to be reduced to 100nF (3dB @ 72Hz).

Also you can use 1uF polyester at the rate of -3dB @ 7.2Hz in case of any general use. However, this adjustment would increase the performance of the bass and you can also apply any value till 10uF (approx.) on C1 if needed to do so.

The new design of the PCB facilitates using the amp as dual-mono. You can split the PCB track while each individual has its own power supply.

While the IMO carries less point, this enables cutting the PCB in half with each halves has its own supply. The board gives the facility to make output connection to the PCB pins, or by using PCB mount spade lug.

Upgrading the Design

As per the board’s design shown in the figure, you can use LM3886. It is very much identical and moreover the specification is higher.

The PCB also have the provision to connect pin number 1 and 5. Furthermore, you can also use the board as a bridge in case of LM3886 to achieve 120W into 8ohms. Our suggestion would be to use P87B to enable out-oh-phase signal that is needed to operate BTL.

To run an amp as inverting is a common occurrence, but doing that ends up with low impedance to the preamp, which may give trouble as you may find distortion or problem in loading. Therefore, it is always safe to drive the amplifiers, since the P87B can drive each amp individually.

Whereas parallel operation is often a common suggestion when building this system, our experience in this domain does not recommend the same.

The requirements for gain tolerance during parallel operation is very strict as you need to ensure the amplifier matches 0.1% or keep it over the entire bandwidth.

Now since the impedance of the IC has low output, therefore even 100mV may end up generating high circulating currents via the IC’s. As 0.1Ω comes as usual suggestion, a mismatch of 100mV may end up 0.5A of circulating current, which ends up in overheating.

Pinout Diagram

Figure above shows the IC pinouts for LM3876 where the pins are staggered to enable the PCB tracks run into the pin of the IC. The LM3886 on the other hand is very much identical to the former, and it can be used by adding little more power, if needed.

However, the only difference that lies between the two is in LM3886 it is mandatory for Pin 5 to connect to +ve supply.

The PCB used for this amp is mainly meant for stereo amplifier. It is single-sided with the location of supply fuse in the PCB. The stereo board contain small four fuses (115mm x 40 mm).

Overall the revised board as in Figure 1.1 is of the same size to that of the original (as shown in Figure 1.0) and we have applied similar spacing in between the IC’s to facilitate retro-fitting, if needed.

However, as a caution do keep in mind to use heat-sink for this project as the system gets really hot within a short time, which may end up destroying the things from overheating.

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Swagatam is an ardent electronic researcher, inventor, schematic/PCB designer, manufacturer, and an avid publisher. He is the founder of https://www.homemade-circuits.com/where visitors get the opportunity to read many of his innovative electronic circuit ideas, and also solve crucial circuit related problems through comment discussion.